Organic polymer chelants for iron and manganese ions

ABSTRACT

PROCESS FOR SOLUBLE POLYMERIC CHELATES OF IRON AND MANGANESE WHICH COMPRISES REACTING IRON AND/OR MANGANESE IONS WITH POLYMERS AND COPOLYMERS BASED ON ORGANIC MONOMERIC ACIDS, THE POLYMERS AND COPOLYMERS PREFERABLY HAVING RELATIVELY LOW MOLECULAR WEIGHTS OF LESS THAN 50,000, THE CHELATION PROCESS BEING APPLICABLE AT A WIDE RANGE OF PH VALUES OF THE ION CONTAINING SOLUTION, COMPOSITIONS OF POLYMERIC CHELATES PREPARED THEREBY AND USES THEREFOR.

United States Patent 3,790,610 ORGANIC POLYMER CHELANTS FOR IRON ANDMANGANESE IONS John C. Lum, Union, N.J., and Ronald F. Beyer, Concord,Calif., assignors to Colloids, Inc., Newark, NJ. No Drawing. Filed Sept.7, 1971, Ser. No. 178,119 Int. Cl. C07f 13/00, 15/02 U.S. Cl. 260-429 JClaims ABSTRACT OF THE DISCLOSURE Process for soluble polymeric chelatesof iron and manganese which comprises reacting iron and/ or manganeseions with polymers and copolymers based on organic monomeric acids, thepolymers and copolymers preferably having relatively low molecularweights of less than 50,000, the chelation process being applicable at awide range of pH values of the ion containing solution, compositions ofpolymeric chelates prepared thereby, and uses therefor.

This invention relates generally to novel chelating agents for ironand/or manganese, to the products produced thereby, and chelationprocesses and uses thereof and more particularly to the use of polymersand copolymers of organic monomeric acids having relatively lowmolecular weights as chelating agents for iron and/or manganese ions toprevent precipitation of solid products thereof.

It is known that various metal ions have the ability to react withorganic compounds especially those having at least two functional orreactive groups to produce a chelate structure or chelate complex withthe metal ions. The formation and chemistry of these compounds has beenwidely studied and developed. These compounds often form insolublechelate structures with selective metal ions thereby giving precipitateswhich can be isolated. In other instances, they react to form solublecomplexes, and are accordingly sometimes called sequestering agents,that is, they hold the ions in solution or suspension. Generally, theorganic chelating agent, usually called the ligand or chelant, is moreor less specific as the chelating agent for one or more metallic ions.This specificity is not predictable except in a very rough way takinginto account such variables as the size of the metallic ion in relationto the molecular size and structure of the chelating groups on theligand.

It is an object of this invention to provide novel chelating agents foriron and manganese ions.

It is another object of the invention to utilize the polymers andcopolymers of certain organic monomer acids to form soluble chelates ofmetallic ions.

Another object is to use polymers and copolymers of such unsaturatedorganic acids as acrylic acid, methacrylic acid, maleic acid and thelike as ligands to form chelates with iron and manganese ions.

A further object is to provide novel organic sequestering agents whichare capable of acting over a wide range of pH values to maintain ironand manganese ions in solution in colorless forms.

Other and further objects will become apparent from a detaileddescription of the invention set forth hereinbelow.

It has been discovered that relatively low molecular Weight organicmonomeric acids form polymers and copolymers which are capable ofchelating with iron and/ or manganese ions to sequester them andmaintain them in solution in colorless form.

The organic monomeric acids which form the basis of the polymers andcopolymers used as the ligands in the invention are of the aliphatic oralicyclic groups and 3,790,610 Patented Feb. 5, 1974 have relatively lowmolecular weight, having from 2 to 8 carbon atoms per molecule. It isdesirable that the monomers have at least one free carboxylic group anda double bond capable of polymerization. Other groups can also bepresent, provided they do not interfere with polymer or copolymerformation, or the chelation reaction, and do not react independentlywith the iron and/ or manganese ions or other ions or materials present.

Typical organic polymeric acids which have been found useful include thepolymers of the acrylic family, i.e., polymers of acrylic acid and itsderivatives. Thus, the organic polymeric acid can be polyacrylic acid,polymethacrylic acid, and the like. Copolymers of monomers of theacrylic family with organic carboxylic acids anhydrides or acid halidescontaining aliphatic carbon-tocarbon unsaturation can also be used.Examples of such polycarboxylic materials include the respectivecompounds of maleic, fumaric, substituted maleic and fumaric such ascitraconic, chloromaleic, and mesaconic; substituted succinics such asaconitic and itaconic and the like. Maleic acid-methacrylic acid andmaleic acid-acrylic acid are typical of the copolymers which are useful.

Other monomer compounds can also be present in the polymers andcopolymers. These include such compounds as ethylene, styrene,butadiene, isoprene, vinyl acetate, acrylates, acrylamide,methacrylamide, and the like.

It has been found important to use such polymers and copolymers havingrelatively low molecular weights. They should have a maximum averagemolecular weight of 75,000 and for best results the average molecularweight should be between 5,000 and 50,000.

The preparation of the polymers and copolymers of the organic monomeracids is readily carried out by processes well known in the chemical andpolymer arts and there is nothing critical in their manufacture for usein the invention. It is, of course, necessary that the molecular weightof the polymers and copolymers be controlled to within the requiredrange. In general, the acid number of the polymer or copolymer is in therange of about 6004000.

The invention has numerous advantages over similar processes andproducts described in the prior art. The process itself is carried outwith readily available chemicals and the requirement for the chelantsused are less per unit of the metal ion, i.e., iron and/or manganesepresent than for other known chelants for these metal ions. The polymersand copolymers used as reactants exhibit and maintain theireffectiveness and prevent the precipitation of iron and/or manganeseions under a wide variation of conditions particularly in mixtureshaving high (above 8) pH values at which values most known and usedchelants for iron and manganese and heavy metal ions generally showreduced chelating power and in some cases are totally ineffective.

In general, these polymers and copolymers of the organic acids have beenfound to be effective as chelants over a pH range of 2 to 14. They havealso been found to function informing chelates and preventingprecipitation of the iron and/or manganese ions when used inconcentrations of about 2 to 20 times the weight of the iron ormanganese ions. Preferably, the concentration is about 5 to 10 times byweight. The concentrations given are based on the total concentration ofall iron and manganese present in the solutions treated. For bestresults, the concentration should be at least 5 times that of theselected polymer or copolymer by weight of the metal present. It is anespecial advantage of these chelating agents that they function well insequestering and maintaining in complete solution even lowconcentrations of iron and/ or manganese ions. They are effective forsolutions having the metal ion concentration as low as one part permillion.

3 4 It has been found that these polymers and copolymers TABLE II of theorganic acids are able to prevent precipitation and Control flocking ofiron and/r manganese ions in t Presence Sample number A B C D (blank) ofvarious other metallic ions such as calcium, magne- Chelant concentratesium, and the like, as well as in the presence of various 5 testSolutiom other impurities and contaminants which interfere with ipi itime or inhibit chelation, complexing or other reactions of Prempmmn23}; V 34 known materials.

These novel chelants for iron and/ or manganese are O again it i to benoted that Samples B, C and D useful in the P p industry to Prevent 1085Of brightness 10 containing known chelants showed precipitates after thebecause of the presence of iron and/01' manganese in the elapse of 18 36hours, and the blank showed precipitate wood pulp. For example, use ofthe polymer ligand in formation in less than 1 minute. The polymericacrylic the ground Wood P p Process for making P p enhances acidprevented completely the formation of a solid prethe brightness of thefinished paper by the more effective cipitate. chelation of iron and/ormanganese. EXAMPLE 3 In connection with the use of caustic sodasolutions, After completion of the fixed high alkaline tests thesechelants can be employed to remove iron complexes such as rust fromsteel or iron surfaces, for cleaning of rust iron phosphates, or theiron compounds from processing equipment where there is danger ofremoval of 20 Sample:

scribed in Examples 1 and 2 the pH of each of the following samples wasadusted to 8.0:

some of the base metal. #l18 g./l. A in 1 g./l. Fe as FeCl Thesechelants can also be satisfactorily used for re- #2-18 g./l. D in 1g./l. Fe as FeCl; moval of light iron oxide films as they hold the iron#3l8 g./l. C in 1 g./l. Fe as FeCl and/or manganese so removed insolution. Each of the three Solutions (2.00

. 1 g.) was titrated with Invention Wm be Illustrate? .m.deta11 by.theconcentrated aqueous NH until a reddish brown precipil examples lalthough It 1s no Way Intended tate formed. The pH was recorded at thepoint when this to hunt the invention thereto. precipitate firstappeared.

EXAMPLE 1 Sample:

A series of comparative tests was carried out to deterp p through P 1133(Over a mine the eifectiveness of various materials as chelation flockor Suspended matel'lal pp to form agents for iron. The chelant of SampleA is polymeric but this 065 not precipitate) acrylic acid having amolecular weight of 32,000, a mate- #zfipreclpltate i Volume at P rialtypical of the invention; Sample B is nitrilotriacetic P 111 Volume at Pacid; sample C is Sodium Salt of ethylene diamifle tetra- Thisexperiment clearly indicates that the polymeric acetic ql al'ld Samp1eis i Pentasodillm Salt of Organic acid of the invention is able tosequester the iron ethylenetrlamlllopelltaacfftlc acldsamples ions at amuch higher pH and thereby prevent formation and the control wereadiusted to a mlmmum P of 11.3 of a precipitate than are the twocompounds (chelants) with NH and ferric ion was added at theconcentration of of the prior art. 1 g./l. as FeCl solution in equalquantity in all cases.

Adjustment was made where necessary to equate the pH EXAMPLE 4 values.In the cases of Samples C and D the pH adjust- Each of the three samplesfrom Example 3 above and ment was not necessary because of the high pHof the two other examples of the invention identified as shown, chelant.was adjusted to pH 8. 0 and maintained there with addi- TABLE I Sample No. A B O D Control blank Chelant H- 1.2 11.3 11.8 11.8 7. 0. Ohelani;coneentration 18 g./l 18 g./l 18 g./l 18 g./l 0.

Km test snhm'nn 11.? 11.3 11.8 11.8 11.3.

nitial appearance Clear dark amber Very turbid Very turbid Very turbidVery turbid. Appearance after standing do Amber w/split. Very lightamber w/split. Light amber wlsplit... Water-white w/split.

Split. Norm heavy 1%" light 1%" light 1%" light.

The results of this test as indicated by the appearance tions of NHwhenever the pH fell below 7.8. FeCl soluof the solutions after standingshows the superiority as -4 i added to each of the 200 8- test S0111 ofSample A, taste... strait.i ginptsnts:ts an in the series. The finalappearance of Sample A is a volume OfFeC13 ineachcase was: clear ambersolution. While all the samples of known chelants includin Sam les B, Cand D usin materials of the prior art ifter s tanding had a tlirbidippearance {ill-400 (suspended.fl9ck but no preclpltate) 5:2-105 cc.heavy precipitate and a split with more or less of two layers. 5 heavyprecipitate These results obtained using known materials in Sam- #4400+cc. flock formed in suspension ples B, C and D are in fact onlycomparable with results flock formed in Suspension The composition ofthe copolymers of Samples 4 and in the control sample or blank to whichno chelatlng or 5 are Shown as follows in Table UL complexing materialwas added.

60 Sample:

TABLE III EXAMPLE 2 Sample number 4 5 The experiment of Example 1 wasrepeated with one Maleic acid, percent 25.0 48.0 Methacrylic acid,percent 35. 5 variable change. The pH was ad usted to 8.2 to make aAcrylamide, arwin.-. 16.5 comparison test with the optimum range for thechelants gt gfgg gg i gggf g 1g "55 of Samples C and D. 75

Sample 4 is a copolymer of maleic acid and acrylic acid and Sample 5 isa maleic acid-methacrylic acid-acrylamide te-rpolymer. Both polymers areof relatively low molecular weights as indicated by their 30% aqueoussolution viscosities shown above.

EXAMPLE 5 The ability of polymeric acrylic acid to remove iron oxidefrom steel in an alkaline media was checked to determine if such aprocess would be feasible.

A solution of 100 g. NaOH/l. and 20 g. of the polymer acid wasformulated and heated to boiling. A length of very rusty steel chain wasimmersed and observed over a one hour period. After one hour rustparticles were noted on the bottom of the beaker and the chain showedevidence of descaling.

EXAMPLE 6 The tests of Example 1 were repeated with the substitutions ofMnSO, for the FeC1 to compare the ability of the invention materials tochelate manganese. It was found that the quantity of precipitate from a1 g./l. Mn++ solution was not sufiicient for comparison so the Mn++ Theabove tests show that Sample A gives no precipitate while Samples B, C,D and E all show evidence of precipitation.

EXAMPLE 7 The tests of Example 4 were repeated with the substitution ofMnSO, for FeCl and the concentration was doubled to 2 g./l. Mn++ tofacilitate a substantial end point. In this case the results were verysimilar to those reported in Example 4.

What is claimed is:

1. A process for rendering and maintaining metallic ions soluble whichcomprises adding to a solution containing metallic ions selected fromthe group of iron, manganese and mixtures thereof, a chelant consistingof a copolymer of maleic acid and acrylic acid and having a molecularweight of less than 75,000.

2. The process of claim 1 wherein the chelant has a molecular weightbetween 5000 and 50,000.

3. The process of claim 1 wherein the treatment is carried out underalkaline conditions.

4. The process of claim 1 wherein the chelant is used at a concentrationof 5 to 10 times the weight of metallic ion present.

5. The process of claim 1 wherein the copolymer conconcentration wasmcreased to 10 g./l. tams 25% maleic acid.

TABLE IV Sample No. A B C D E (control) Chelant concentrate 18 g./l 18./l 18 /l 18 all 0. Neutral pH in test 11.3" 11.8 113 11.3, Initialappearance Milky white White flock whit flock White flock Wh1tefl0ck.Appearance on standing .do Tan precipitation Tan precipitation Tanprecipltatlon. Brown preclpltatlon. Split NMP heavy heavy W h avy heavy-References Cited UNITED STATES PATENTS 3,055,873 9/1962 Hull et al.260-784 R 3,285,886 11/1966 Gunderson et al 210-58 3,405,060 10/1968-Carter et al. 210-58 3,463,730 8/1969 Booth et al 252-180 3,514,376 5/1970 Salutsky 252-180 3,578,589 5/1971 Hwa et a1 252-180 3,663,4485/1972 Ralston 252-180 3,085,916 4/1963 Zimmie et al. 210-58 FOREIGNPATENTS 31,015,612 1/l966 Great Britain. 1,068,037 5/ 1967 GreatBritain.

DANIEL E. WYMAN, Primary Examiner A. P. DEMERS, Assistant Examiner US.Cl. X.R.

134-3; 210-58; 252-180; 260- L, 80 P, 439 R

